Middle-age memory loss may be inherited from parents with Alzheimer's, according to research at the University of Boston.
It cites the gene ApoEe4, which appears to make carriers three times more susceptible to mental impairment if a parent had suffered from dementia.
Study author, Dr Stephanie Debette, says: "The effect was largely limited to those who have the ApoEe4 gene, which supports the idea that the gene is probably at least partially responsible for the transmission of Alzheimer's disease risk between generations.
"However, all of these individuals were functioning normally, and only further testing can determine whether the poorer performance on memory testing in middle age would lead to an increased risk of developing Alzheimer's disease or other dementia later in life."
The findings will be presented at the American Academy of Neurology's annual meeting in Seattle later this year.
Professor Clive Ballard, Director of Research at the Alzheimer's Society, said: "This is an interesting study as it suggests that individuals who have the ApoEe4 gene and a parent with dementia are more likely to have some memory impairment in mid-life. It is not yet clear whether they would go on to develop Alzheimer's."